8.2
上皮組織とその機能
上皮組織は、身体のあらゆる表面を覆う大きな細胞シートです。これらの表面は、皮膚、気道、消化管、尿路系、生殖系など、内部または外部に存在することがあります。血管や漿液膜などの身体の外部とはつながっていない中空臓器や体腔は、内皮として知られる上皮組織によって内張りされています。
上皮組織は、物理的、化学…
上皮組織は、体を覆い、特定の環境を区画化して病原性の侵入、体液の損失、または機械的損傷から体を保護する密集した細胞のシートです。
それらは、上皮を覆うまたは覆う上皮と腺上皮の2つの形態で発生します。
上皮を覆うか裏打ちするかは、ゲートキーパーとして機能します。それらは露出した体の表面を覆い、臓器の内管を覆い、選択的な物質が体に出入りすることを可能にします。
例えば、腎臓尿細管の上皮内層は、尿からの栄養素の再吸収および近くの毛細血管からの老廃物の放出を可能にする。
腺上皮は、単一の細胞または細胞のグループであり得る特殊な構造または腺に配置されています。それらは、粘液、汗、ホルモンなどのさまざまな分泌物質を生成および放出します。
上皮組織には、外部環境と内部環境の間で情報を素早く中継する感覚神経が豊富に供給されており、即時の反応を生み出します。
たとえば、蚊に刺されると、皮膚上皮の下の神経が即座に刺激され、体がその場所に叩くように引き
起こされます。Q1: What are the two main types of epithelial tissues and how do they differ?
Epithelial tissues exist as covering or lining epithelia and glandular epithelia. Covering or lining epithelia function as gatekeepers, covering exposed body surfaces and lining internal organ tracts while allowing selective substances to enter and exit. Glandular epithelia are specialized structures arranged into glands that produce and release secretory substances like mucus, sweat, and hormones.
Q2: How do epithelial tissues protect the body from harm?
Epithelial tissues form protective sheets of closely-packed cells covering body surfaces and lining internal tracts, shielding the body from pathogenic invasion, fluid loss, and mechanical injuries. They act as the body's first line of defense against physical, chemical, and biological wear and tear. All substances entering the body must cross an epithelium, making it a critical barrier.
Q3: What role do sensory nerves play in epithelial tissue function?
Epithelial tissues are richly supplied with sensory nerves that quickly relay information between external and internal environments, producing immediate responses. For example, a mosquito bite instantly stimulates nerves under the skin epithelium, triggering the body to swat at the location. This rapid sensory feedback helps protect the body from threats.
Q4: How do epithelial cells contribute to digestion and respiratory defense?
Many epithelial cells secrete mucus or other chemical compounds with specific functions. The intestinal epithelium releases digestive enzymes to help break down food, while the respiratory tract lining secretes mucus to trap incoming microorganisms and particles. These secretions support both nutrient processing and pathogen defense.
Q5: What is selective transport and why is it important in epithelial tissues?
Epithelial tissues act as gatekeepers by allowing selective transfer of materials across a physical barrier. For instance, the epithelial lining of kidney tubules allows reabsorption of nutrients from urine while releasing waste products from nearby capillaries. This selective permeability ensures the body retains essential substances while eliminating waste.
Q6: How are glands structured and what do they produce?
Glandular tissue consists of single or multiple secretory cells that yield a variety of secretions. These glands can be unicellular or multicellular structures that discharge secretions either on the epithelial surface or into the bloodstream to reach target cells. Common secretions include mucus, sweat, digestive enzymes, and hormones.
Q7: Where are epithelial tissues found throughout the body?
Epithelial tissues cover all body surfaces, both internal and external, including skin, airways, the digestive tract, urinary system, and reproductive system. Hollow organs and body cavities not connected to the exterior, such as blood vessels and serous membranes, are lined by specialized epithelial tissue called the endothelium. This extensive coverage ensures comprehensive protection and selective transport.